Extrusion molding



June 18, 1946. L. B'. GREEN EXTRUsIoH- HOLDING Filed oct. 11, v1943 wwwINVENTOR. EE E GREEN BY im www @Wb/w ,4r Tae/vers NN MN Patented June18, 1946 UNITED 'STATES lurrls;urA OFFICE 1 l 2,402,2sr l lflf'flos301mm. (ol. is-iz) 'I'his invention relates to the molding of plasticmaterial and more particularly to a novel method and apparatus forextruding such material in a more eiilcient and satisfactory manner thanhas been possible heretofore.

The extrusion of plastic material provides a very rapid and economicalway oi producing-certain products such as strip material moldings,tubing and the like. However, when the product to be extruded hasrelatively thick and thin portions, that is to say, is ribbed or is ofan irregular cross-section considerable difficulty is experiencedbecause of the tendency of the product to become bowed or bulged duringthe extruding operation.

This tendency for the product to become bowed or bulged results'from thefact that with a given pressure applied to the plastic material toextrudethe same, the material will ow through the die portionscorresponding with the relatively thick portions of the product at afaster rate than through the die portions corresponding with the thinportions of the product. Attempts have been made to overcome thisdifficulty by conveying the extruded products away from the extrudingdie at an increased rate of speed, but so far as I am aware, this hasproven unsatisfactory because it tends to stretch and weaken'therelatively thin portions of the product.

Aimed at the elimination of the above mentioned difficulties, my.invention provides a novel method and apparatusl for extruding plasticmaterial in a manner which prevents such bowing or bulging byappropriately controlling the ow of the material through the extrudlngdie or oriilce.

other object of my invention is to provide a novel method and apparatusfor extruding plastic material in which the ow of the material throughcertain portions of the extruding die is retarded relative-to the flowthrough other portions to obtain a substantially uniform rate of ow forall portions of the die.

Still another object of this invention is to provide a novel method andapparatus for extruding plastic material to form a product havingrelatively thick and thin portions, in which retarding means in the dieportions corresponding with the relatively thick portions of the productretard the now therein relative to the flow in the die portionscorresponding with the relatively thin portions of the product,sunlciently to obtain a substantially uniform rate of ilow for allportions 0i the die.

Other objects and advantages oi the invention ing a converging passage2| therein which, at its will be apparent from the following descriptionwhen taken in commotion with the accompanying sheet of drawings in whichFig. 1 is an end view of extruding apparatus constructed according to myinvention and with which my novel method can be carried out;

Figure- 2 is a longitudinal sectional view of the apparatus taken online 2 2 of Fig. 1, and

Fig. 3 is an end view of a modiiiedform of my extruding apparatus.

For a more detailed description of my invention further reference willnow be made to Figs. 1 and 2 ci the drawing in'which I show one form ofmy-novel extruding apparatus it, This extruding apparatus comprises, ingeneral, an extruding die Il and a cylinder I2 adapted to containingplastic or thermoplastic material i3. A plunger lil operable in thecylinder subjects such material to pressure for discharging the samethrough the reduced portion I2a of the cylinder and through theextruding die il as further explained hereinafter.

The cylinder I2 is contained in a body l5 which vis suitably supportedand forms a part of a conventional iorm of extruding apparatus. Aheating coil I6 disposed around the wall of the cylinder i2 suppliesheat to the material it' torender the same plastic and workable. Thermalinsulation Il, located around the coil It retards the loss of heattherefrom. As is usual in apparatus of this kind, the cylinder i2 mayhave a spreader i8 supported therein by a web or rib lil and 10- catedso as to crowd or deflect the plastic material toward the side walls ofthe cylinder where it will be more effectively heated by the coil I6.

The material I3 may be any plastic material which is capable of beingextruded, although the invention is especially applicable to extrudingoperations using a thermoplastic material, such as the material known astenite The extruding die I I comprises a die block havdelivery end ororifice 22, is of a cross-sectional shape corresponding to that of theproduct 23 to be extruded. In this instance the product 23 is a strip'ormolding having a relatively thin iiange or web portion 23a and arelatively thick longitudinal rib or bead portion 23h. As shown in Fig.1 the orifice 22 is of a corresponding shape, that is to say, it has aslot-like portion 22a which forms the web portion 23a of the product andan enlarged portion 22h which forms the longitudinal rib or bead 22h ofthe product. The extruding dieL Il is bolted or otherwise connected withthe delivery end ofthe cylinder-containing body 3 l5, so that theconverginz passage 2l forms a smooth continuation of the convergingportion l2a of the cylinder.

As pointed out above in a general way, when the plastic material i3 issubjected to pressure by the plunger la so as to discharge the materialthrough the extruding die Il to form the extruded product 23, thematerial will ow more readily through the rib forming portion 22h of thedie than it willl through the web-forming portion 22a. The reason forthis is probably that the area of contact between the plastic materialand the die is much greater in the die portion 22a in relation to thevolume of plastic material than it is in the die portion 22h. Suchrelatively larger surface area in relation tothe volume of plasticmaterial causes the frictional drag or adhesion between the material andthe die surface to retard the flow of the material through the dieportion 22a in relation to the flow through the die portion 22h. Unlesssuch variation in the rate of flow of the material through therespective die portions 22a and 22h can be prevented, the more rapid owthrough the die portion 22h will cause the extruded product 23 to assumea bowed or bulged condition.

For the purpose of overcoming this undesirable effect in extruding, Iprovide the die Il with retarding means by which the now of materialthrough the die portions 22b'can be slowed or retarded sumciently, sothat for a given pressure exerted on the plastic material i3 by theplunger I4, the rate of flow through the ,die portions 22a and 22h willbe substantially equal or uniform. This retarding means is here shown inthe form of a pin 25 which extends partway into passage 2l at a pointinwardly of the orifice 22. In this instance the pin 25 is ofsubstantially circular cross-section and has a rounded inner end Zaalthough the shape of the pin can be varied according to therequirements of the extruding die and the cross-sectional shape of theparticular product being extruded.` The pin 25 may also have a threadedstem 28 and a head 2l and it may be mounted in a relatively inclinedopening in the die il so that the head will be readily accessible andwill enable the stem to be rotated for adjusting the extent to which thepin projects into the passage 2l. A lock-nut 28 is provided incooperation with the threaded stem 2d for locking the pin at the desiredsetting.

The pin 25 projects into the die passage 2l as above explained, extendsinto the stream of the plastic material being forced through the passageand orifice and retards the flow of such material through the portion ofthe passage and orifice in which the pin 25 is located. In this instancethe pin 25 extends into the die portion 22b as shown in Fig. 1 andretards the flow of the plastic material in this portion of the dieWithout materially affecting the rate of flow' in which such pin islocated. As the result of the retardation produced by the pin 25 theflow of material will take place at a substantially uniform rate throughall portions of the die Il and bowing or bulging of the extruded product23 will be prevented. It will be understoodl of course, that afterpassing the pin 25 the stream the distance which the pin is spacedinwardly from the orifice can be varied as required by the particularmaterial andl product being extruded.

In Fig. 3 ofthe drawing I show another form of my extruding apparatus inwhich the extruding die 30 is similar to the extruding die Il but has apassage and orifice 3| of a somewhat different cross-sectional shape andwhich forms the extruded product 32. The product 32 is a strip ormolding having a longitudinal rib or bead 32a along one side thereofcorresponding with the rib or bead 22h of Fig. l and another rib orenlargement 32e spaced from the rib 32h, The extruding die 3@ isprovided with a plurality of the retarding pins 33 and 34 which aresubstantially extruded without such product having a tendency to becomebowed or bulged. It will be seen also that by the use of retarding meansin the extruding die, as above explained, a substantially uniform rateof flow is obtained for the plastic material through all portions of theextruding die and the product extruded therefrom will accordingly remainin a straight and unbulged condition.

While I have illustrated and described my novel extruding method andapparatus in more or less detail it will be understood, of course, thatdo not wish to be correspondingly limited but regard my invention asincluding all changes and modifications coming within the scope of theappended claims. l

Having thus described my invention, I claim:

1. The method of molding thermoplastic material to produce a product inthe form of a strip having a cross-section which includes relativelythick and thin portions, comprising the steps of subjecting heatedthermoplastic material to pressure so as to extrude said material at adesired rate through a die opening havingl relatively wide and narrowportions corresponding with said thick and thin portions of the product,and retarding the flow of said material only in the relatively wideportion of the die opening such that the flow of said material producedby said pressure will be at said desired rate for both the wide andnarrow portions of the die opening.

2, In molding apparatus, an extrusion die for delivering a product inthe form of a, strip having a cross-section which includes relativelythick and thin portions, said die having an orifice and a passageleading to said orifice, said orifice havlng relatively wide and narrowportions corresponding with said thick and thin portions of the product,means for subjecting heated thermoplastic material to pressure fordischarging such material at a desired rate through said passage andorifice to produce said product, and flow retarding means associatedonly with said relatively wide portion of said orifice so that the flowof said material produced by said pressure will be at said desired ratefor both the wide and narrow portions of said orifice.

3. In molding apparatus, an extrusion die for delivering a product inthe form of a strip having a cross-section which includes relativelythick conforms to the shape of the orifice 22 and that 75 and thinportions, said die having an orifice and a passage leading to saidounce, said orm having relatively wide and narrow portions correspendingwith said thick and thin portions of the product, means for subjectingheated thermoplastic material to pressure f or discharging such materialat a desired rate through said passage and orifice toproduce saidproduct, and flow retarding means associated only with said relativelyWide portion of said orifice so that the flow oi said

